Help!I have a 2wd 1988 sapphire cosworth which has a big flat spot from idle.It starts fine but when I stab the throttle it almost cuts out,but when I feed the throttle in slowly it revs ok.I`ve replaced the ecu and put a new chip in,replaced the ignition module,new fuel pump and filter any ideas ?

 

tbh m8 that could be caused by a whole heap of reasons ie badly being set up,worn or out of adjustment tps,air leak the list could go on imo!

 

I'd borrow a map sensor and swap it over , always good to try the sensors first as normally can swap over from a buddy's car in a few minutes and you learn a bit about your car along the way

 

TPS would be my bet, the most common place for it play up as well, just above idle as most worn area, put a metre on the tps and take readings, you may well be able to hit the missing point opening the throttle slowly, and this would confirm it.
I would also check the CO, isn't a tad lean, set to around 2-2.5%.
tabetha

 

had a similar prob tab with a buddies car and went straight for the tps as well, after lots of fiddly swapin of l6/l8 tps s i swapped the map sensor and it ran sweet as a nut.had also swapped every other sensor in the bay by that stage.for some reason thought map would not produce that fault....

 

I`ve replaced the map sensor,spark plugs QC57 ,checked the tps resistance and seemed ok,adjusted the phase sensor gap (was 0.55mm now set to 2.5mm.replaced coil (put old coil back as no different).It is a lot better now and the flat spot gets less as it warms up,after approx 10-15 minutes (bear in mind that i`m in oz and it`s 22 degrees at 6 in the morning).Now it`s just a very small flat spot.I think I`ll get a tps and rule it out ,need a spare anyway.I`ll let you know how I get on unless you have any other suggestions!

 

What's the engine spec?? IF it's NOT 400+ bhp then your using the wrong plugs if it's Champions your still using you want to be using a set of QC59C!

 

Used 59c plugs till I learned better, they foul up something terrible si have used STD ford 071s on specs from STD to 400brake,no fouling or misfires
Gap type coil is a good replacement for STD ford coil if that's what's fitted,will be old at this stage plus gap type gives about 2.5 times the output......
Rob v

 

Try some better plugs, they may well be too cold, I'd suggest some IK31.
tabetha

 

Tabs ,

What's your experience with fords 071s, only £10 a set and very reliable I find.

What are ik31s

 

071 are fine, a very good versatile plug that will do the job perfectly, just not as perfect as some others, the IK range are made by Nippon Denso, they have a iridium centre electrode, and take less voltage to create a spark, despite iridium being a bad conductor!!
My experience of iridium plugs is a better more stable idle, smoother running, and just seen generally more eager on them, the downside I found is they hate being fouled and often throw in the towel if sooted, even once cleaned often don't work 100% again, but so long as mixture correct isn't a problem, around 4x the cost but worth it imo, others may not agree, it is a lot of difference £10 or £40, so I can see their point, your choice really.
I'm using 071 for running in, but will change around 1500 miles.
tabetha